Attitudes to trade unions are surprisingly difficult to pin down: different surveys give very different results, partly according to the precise question asked, and attitudes seem to fluctuate with bewildering speed. It is even harder to establish trends historically (before the development of modern survey methods). Eurobarometer surveys show a wide variation in attitudes across countries, with Britain around the middle of the distribution. In fact the autumn 2014 survey shows that 57% of UK respondents reported a positive view of trade unions.
To the extent that British people are indeed suspicious, two factors strike me as important:
First, only one worker in four today is a union member (compared to half the workforce 40 years ago). So most of the public have no direct experience of trade unions. This means that they are likely to depend for their information (or misinformation) on a press which in the main is unremittingly hostile to trade unionism.
Second, trust in most institutions has been declining over time. Indeed, surveys often reveal far greater trust in trade unions than in business leaders, the media and politicians.